The present invention relates to a method for the determination of stress applied to a steel material constituting a structural body in the fields of architecture, civil engineering, machinery and the like. More particularly, the invention relates to a reliable and rapid non-destructive method for the determination of the principal stress and the direction thereof in a steel material.
Several methods utilizing magnetism are known in the prior art for the determination of a stress applied to a steel material including a method by utilizing the changes in the magnetic permeability caused by the stress and a method utilizing the changes in the Barkhausen noise caused by the stress. The former method utilizes the principle that the magnetic permeability varies in proportion to the difference in the principal stresses for the determination of the principal stresses and the directions thereof. The latter method utilizes the principle that the Barkhausen noise is varied corresponding to the principal stress for the determination thereof.
The above mentioned conventional magnetic methods for the stress determination each have a problem in the reliability. For example, no reproducible results can be obtained due to the phenomenon of hysteresis inherent in the magnetic measurements. Since the measurement is performed in the range of the magnetic field which is approximately of the same order as the coercive force of the steel materials, in addition, a large error is unavoidable in the result of the determination when the steel material has residual magnetizatism. Moreover, each of these prior art methods is an empirical method merely based on the observed facts with no established theoretical ground so that the methods are subject to a limitation relative to the versatility in the application to a variety of materials.